Spider silk is an ancient biomaterial that is tougher than steel, yet elastic and light weight. The superior physical properties of spider silk make it an attractive biocompatible functional material. Various applications of silk in water collection, biomedical devices and optics have been demonstrated. Silk fibers with enhanced toughness and possessing electrical and magnetic properties have been created by infiltrating them with various (non-) metallic nanoparticles. A great deal of experimental and theoretical efforts has been made to understand relation between structure and its functional properties. However, to realize true potential of silk for diverse nanoengineering, technological and other applications two fundamental difficulties exist. First, it is difficult to manipulate the silk with nanoscale precision due to high toughness and finesse. One needs to devise a noninvasive nano-processing approach for silk while preserving its key structural building blocks and also retaining its excellent physical properties. Second, it is not yet fully explored, how to integrate silk with other modern materials such as metals, dielectrics, synthetic polymers thereby combining their best properties. Thus, it is vital to devise a new approach to remove these two bottlenecks.
Previously, chemical processing techniques have been proposed to make silk films and bulk structures for various applications. Ablation of spider dragline by nanosecond (ns) pulses of deep ultraviolet (VUV) radiation has also been studied. Moore et al., in 2006 made a first attempt to process the dragline silk of black widow spider (Latrodectus hesperus) using nanosecond UV laser (λ=157 nm) under vacuum controlled conditions. Besides requiring high vacuum conditions, the VUV light degraded the silk structure leading to loss of function and strength. Thus, it is apparent that it is difficult to nano-machine silk fibers in controlled conditions. Moreover, it is difficult to micro-weld silk fibers such as spider silk with themselves or other materials.
Recent advent of amplified ultrafast lasers has drawn considerable interest for material processing. These lasers could provide higher precision and less thermal damage than conventional lasers with rather long pulse durations of several tens of nanoseconds. Ultrafast lasers are very efficient for direct micromachining of materials because of their non-contact nature, which allows micro-processing and surface patterning of materials with minimized mechanical and thermal deformations by rapid pulse energy deposition. Since last decades, short femtosecond (fs) pulses have evolved into a preferred tool over picosecond (ps) and nanosecond (ns) pulses in precise material processing with low collateral damage. Femtosecond (fs) lasers have made a mark to be used in corneal refractive surgery and many more surgical procedures. The effects of different fs-laser parameters such as pulse energy, wavelength, pulse width, and tissue depth on the operation performance have been widely investigated. But, fs-lasers processing technology has not been used yet to fuse/weld threads/fibers/sutures that holds the donor tissues in place during healing. Fs-lasers could be proposed as a future surgical tool for seamless micro-welding for joining biological tissues including cornea. Therefore, it is a vital need to establish an optical approach to modify threads/fibers/sutures and micro-weld on surfaces using such lasers.
The present invention is an attempt to overcome problems in the prior art and for the first time shows that the interaction of spider silk with few-cycle fs pulses generated by fs lasers offers a unique opportunity for its controlled nanoprocessing and heterostructuring with diverse materials in air. Precisely, in order to overcome limitations in the prior art, the inventors have developed femtosecond laser based framework to modify and weld (seamlessly) the thin silk fibers with a high precision. This is a significant step to realize spider silk fibers and other natural fibers in utilization as threads/sutures for fabricating nano-devices, allografting, designing pressure, force and vibration sensors.